Comment: 19:37 - 20:27 (00:50)
Source: Annenberg/CPB Resources - Earth Revealed - 10. Geologic Time
Keywords: "radiocarbon dating", carbon-14, radioactivity, carbon, atmosphere, water, plant, animal, isotope, "absolute age dating"
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Our transcription: The carbon in air and water is made up of three different isotopes.
One of these, carbon-14, is radioactive.
As part of the atmosphere carbon-14 is absorbed by living plants and animals.
In this way, the carbon in all living organisms contains the same proportion of carbon-14 to non-radioactive carbon.
When the organism dies, it stops taking in any new carbon, and the amount of carbon-14 inside it gradually decreases as it decays.
It is this shrinking proportion of carbon-14 that tells us how long ago the organism died.
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Geology School Keywords
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